1. Field of the Invention
This invention relates to a control device for a vehicle generator and more particularly to a load responsive control device for an alternating current (AC) generator to be installed in a motor vehicle carrying a battery.
2. Description of the Prior Art
In a prior art control device for a motor vehicle alternating current generator, an output voltage of the generator or a voltage across a vehicle battery is divided by utilizing a voltage divider made up of resistors and the like, and a divided voltage is compared with an output voltage of a standard voltage generator a zener diode to generate a control signal. The output voltage of the generator is then regulated to keep a required value by switching a switching element connected in series with a field coil of the generator for controlling a field current that flows therethrough based on the detected control signal. That is, if the output voltage of the generator is higher than the set voltage, the switching element is turned off to decrease the field current whilst if it is lower than the set voltage, the switching element is turned on to increase the field current, whereby the output voltage of the generator is maintained at the set voltage. In such a control device of the type as described above, there is provided a continuous change of field current to follow up, with a time constant of the field coil (approximately 100 msec), a fluctuation of the required field current of the generator caused by a fluctuation of an electric load and the like, and a stabilized control of the battery voltage is attained through such response.
However, in the prior art system, because of such rapid response, an output current of the generator may change abruptly in a fluctuation period of an electric load, which may cause an abrupt change in driving torque (power). This in turn results in a problem of causing a change of the rotary speed of an engine, especially, in a range of idling of the engine whereby a driving power of the engine is decreased to a great extent. Therefore, a reciprocal increase of driving torque of the generator under such condition may cause serious problems.
It is therefore an object of this invention to solve the aforesaid problems and to prevent an abrupt change in driving torque of the generator caused when an electric load is applied thereon, to provide a control device capable of restraining a rotary fluctuation of the engine.